Z E O
ZIN
( 4 96 )
radiated, approaching on one hand to foliated,and on the other to' fibrous. It prefents longifhgranular diftindt concretions. It is tranflucent,palling into tranfparent, and poffelfes a doublerefraction. Its hardnels is fomewhat fuperiorto that of calcareous fpar; it is brittle andeafiiy frangible. Sp. gr. 2.03 — o n8.
Before the blow-pipe it intumefces and meltslike borax. It is foluble in the mineral acids,and forms with them a gelatinous mafs. Itscomponent parts, according to V auquelin, are50.24 Silex29.3 Alumine9.46 Lime10. Water
99.
Tt paffes into the two following varieties.
Var. 1. Fibrous Z. Fafriger Z. Worn.
Its colours are nearly the fame as the pre-ceding, except that it fometimes occurs wax-yellow and greenifh-white. It occurs in mafs,reniform, and in capillary cryltals. Its fradture■is divergingly fibrous, palling into fplintery. Inother refpedts it agrees with the preceding.
Var. 2. Mealy Z. Mehlzeolith, Wern.
Its colours are yellowilh and reddilh-whitepalling into flelh-red. It occurs malfive, coral-loidal, and incrulting other zeolites. It is dull;its fra&ure is coarfe earthy, approaching tofinely fibrous. It is opake; very foft, almoftfriable; very light; and when rubbed with the•nail it gives a grdting feel and noile like burntbrick.
2. Sub/p. Lamellar Z. Blattriger Z. Wern.'Stilbite Hauy.
Its colour is yellowilh and greyilh-white,rarely reddilh-white. It occurs maflive, globu-lar and cryftallized. Its primitive form is arhomboidal pril'm: the other varieties that itprefents are, a fhort hexahedral prifm, theoppofite faces alone of which are equal; and atable of fix equal fides. The cryftals are fmalland middle-fized, and their furface is alwaysfmooth and Ihining. Internally its 'lultre isftiining and pearly. Its fracture is lamellar,generally fomewhat curved, and is divilible onlyin one diredlion. It prefents granular andfometimes curved lamellar diftindl concretions.
> When in mafs it is tranflucent, and when cryf-tallized is generally tranfparent. In its othercharacters it refembles the preceding fub-fpecies.
It is compofed, according to Vauquelin, of
52. Silex
17.5 Alumirte9. Lime
18.5 Water
97 -
3. Sub/p. Cubic Z. Wurfel Z. Wern.Analcime & Chabajie Hauy.
Its colour is greyilh, and yellowilh-white,and yeilowith-brown. It occurs in mafs andcryftallized. The primitive form of its cryftalsis a hexahedron approaching very near to acube; fometimes each folid angle of the cubeis replaced by an obtufe trihedral pyramid fetupon the*faces of the cube : fometimes thefefecondary faces are fo large as to obliterate thofeof the primitive cryftal, whence there refults afolid with 24 trapezoidal faces. The cryftalsare fmall and middle-fized, and are brightlyfhining externally with a luftre between vitreousand pearly. The internal luftre is fomewhatinferior to the external. Its fradture is imper-fedtly lamellar in three directions, paffing fome-times to uneven. Its fragments have a ftrongtendency to the cubical form. It prefents gra-nular diftmct concretions; is tranflucent, paffingto tranfparent; is fomewhat harder than glafs.Sp. gr. 2.7.
It intumefces before the blow-pipe, but doesnot gelatinize with acids.
Zeolite occurs principally in the moll recentfloetz trap-formation, efpecially in amygda-loid and cellular bafalt; in thefe rocks it fome-times only lines, but often entirely fills up thecavities which they contain. It alfo occurs,though rarely, in primitive greenftone, and inveins accompanied by galena.
All the above fubfpecies occur in Scotland ,but the largeft and molt beautiful fpecimenscome from Iceland and the Ferroe Iflands:they are alfo met with at Adelfors in Sweden ,in various parts or Germany , and very abun-dantly in the South Sea Iflands.
ZINC. ZJnk, Germ. Zinc , Fr. Spelter ,Tutenag, of the Chinefe.
Zinc is a bluilh-grey femi-dudtile metal ,fufible at lefs than a red heat, and combuftibleat the loweft point of ignition, an extremelybrilliant bluifh-white flame being given out, andthe metal being converted into a white floccu-lent oxyd.
Sp. 1. Common Calamine, Native carbonatof Zinc .
Of this mineral there are the three followingfubfpecies.